Welcome to PHPBuilder. 🙂
MAMP, I assume, is a Mac OSX PHP environment?
Where are the logfiles on Mac? BSD (from which OS X gets its roots), holds server log files under /var/log. Do you have a file that looks like an HTTPD error_log file under /var/log? If so, look and see what's in it after you try to load your page.
Does which php in your terminal give any result? What about php -r "echo 'foo';" ?
Also, if you're not getting anything to work at all, try something simple for your first script, like:
<?php
echo "First script!";
?>